BACKGROUND: Most of the current licensed viral and bacterial vaccines produced in the world are in the state of antigen suspension, and the immunogenicities of the vaccines can be maintained for one to two years at 4 degrees C, but without refrigeration vaccines easily lose their immunogenicities. METHODS: In this study, as an attempt to improve the stability and maintenancee of the immunogenicity of the vaccines at room termperature or at higher temperatures, sucrose, lactose and glucose were added into the leptospira vaccines respectively, and kept at 37 degrees Cfor 1, 3, 5, and 7 days. The vaccines were inoculated twice into Sprague Dawley rats after 7 days' interval and the titers of the antibodies against the antigen of Leptosp ira icterohemorrhagiae in the sera from rats were measured. Results were evaluated by logistic regress analysis (SAS/PC). RESULTS: Sera from rats inoculated with the normal contol vaccine kept at 4 degrees Cfor 7 days showed antibody titers of 1:20 ~80. The vaccine without sugar exposed at 37 degrees Cfor one day nearly lost its immunogenicity. And the vaccine contained sucrose could keep the immunogenicity at least for 7days at 37 degrees C(p=0.001), though the titers were slightly lower than the titer of normal control. Stabilities of lactose and glucose were lower than sucrose. CONCLUSION: Addition of sucrose, lactose and glucose could increase the stability of leptospira vaccine. 7.5% and 10% sucrose in vaccine could maintain the immunogenicity of leptospira vaccine for 7 days at 37 degrees C. This method is expected to be applied to the production of other viral and bacterial vaccines.